# Triangularity

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The triangularity refers to the shape of the poloidal cross section of the Last Closed Flux surface (LCFS) or separatrix of a tokamak.
Assuming^{[1]}:

*R*is the maximum value of_{max}*R*along the LCFS or separatrix.*R*is the minimum value of_{min}*R*along the LCFS or separatrix.*R*is the geometric major radius, defined as_{geo}*(R*._{max}+ R_{min})/2*a*is the minor radius of the plasma, defined as*(R*._{max}- R_{min})/2*R*is the major radius of the highest vertical point of the LCFS or separatrix._{upper}*R*is the major radius of the lowest vertical point of the LCFS or separatrix._{lower}

The upper triangularity is then defined as follows:

and similar for δ_{lower}.
The overall triangularity is defined as the mean of δ_{upper} and δ_{lower}.

## See also

## References

- ↑ T.C. Luce, Plasma Phys. Control. Fusion
**55**(2013) 095009